Light beer is ceding ground as cabernet-loving baby boomers and millennials weaned on exotic cocktails seek more complex flavors in their brews. High unemployment among light beer drinkers has prompted some to drink less or switch to cheaper brews. In a bid to return the froth to light beer, the U.S. joint venture between Molson Coors and SABMiller unveiled new advertising for a key brand, Miller Lite.

If the companies can’t revive the brand, “we’ve got big trouble ahead of us,” said Bump Williams, whose BWC advises more than 100 beer retailers. “Light beer has become a commodity.”

The new Miller Lite ads will revive the brewer’s classic tagline, “It’s Miller Time.” Aimed at men in their 20s and 30s, the campaign will tone down talk of carbs and calories in favor of a “brewed for brotherhood” theme. The brand will spend 50 percent more on media in the summer season.

“Miller Time is all about real friends getting together over a real beer,” MillerCoors Chief Marketing Officer Andy England said. “We’re going to articulate that with a kind of Midwestern grit that can only come from Miller Lite.”

Light beer, an American invention, took hold in 1975, when Miller Brewing Co. became the first to distribute a low-calorie beer nationwide. Four of the five best-selling suds in the U.S. are light beers.

Still, as consumers turn to more exciting alternatives, U.S. beer sales volumes have dropped for three straight years, including a 1.5 percent decline in 2011, according to the Beverage Information Group. Coors Light — the only Top 5 U.S. beer still growing — posted a 1 percent increase last year, the same as in 2010.

The shift has retailers stocking more wine and spirits. Beer lost 2.3 share points of display space in the past five years as spirits and wine gained, according to Nick Lake, senior director of category management for Heineken.

Miller Lite has always sought broad appeal, with early TV ads featuring athletes pitching the brew as “Everything You always Wanted in a Beer. And Less.” New York Yankees baseball legends George Steinbrenner and Billy Martin later argued over whether it was better to say the beer “tastes great” or was “less filling.”

By the mid-2000s, craft beer’s rise made it harder for light beers to make a case for taste. They tried anyway. In 2008, Miller Lite brought back the “Great Taste, Less Filling” idea in its advertising amid falling sales. The following year, Miller Lite advertised itself as “triple hops brewed for great pilsner taste,” as more Americans discovered more heavily hopped craft beers such as New Belgium Brewing Co.’s Fat Tire. Miller followed that up with its “Taste Greatness” campaign. Sales didn’t recover.

The industry also has attempted to juice sales with packaging innovations, such as wide-mouth screw top cans, aluminum bottles and wide-mouthed vented cans. Now Anheuser is turning to higher alcohol content with Bud Light Platinum, featuring 6 percent alcohol, compared with 4.2 percent for regular Bud Light.